1. Field of the Invention
The present invention relates to a light-diffusing reflector for electrooptical displays, especially for displays which are based on the principle of the nematic liquid crystal rotating cell, and in particular a reflector constructed of a foil, the reflecting surface of which has a first structure determined by furrow-shaped depressions arranged in a preferential direction.
2. Description of the Prior Art
Nematic liquid crystal rotating cells are understood to be mainly polarization modulators. Two polarizers in this case make the modulation of the surrounding light visible to the eye. In order to achieve a good contrast in a display based on the principle of the liquid crystal rotating cell and operated by reflection, it is necessary to provide behind the rotating cell provided with polarizers a reflector with a high reflective capacity and also with suitable diffuse scattering power.
Such reflectors consisting of two aluminum foils pressed against one another are used because of their low price and the reflective and scattering capacity which is sufficient for many applications, by many manufacturers in the production of displays which are based on the principle of the nematic liquid crystal rotary cell.
Since in the case of these reflectors the matted structure necessary for an adequate light diffusion is produced on the insides of two comparatively soft foils, for example aluminum foils with a thickness of 6 to 40 .mu.m, which lie on top of one another and can be moved through the gap formed between two opposite rollers, this matted structure has furrow-shaped depressions approximately uniformly aligned in a preferential direction provided by the direction of movement of the rolled foils. This structure has the effect that the surface of the aluminum foil is optically anisotropic, and that the incident light is reflected at varying intensity depending upon the azimuth angle, as a result of the large proportion of regular reflection, so that when the display (and consequently the reflector) is turned round to azimuth, an observer will observe different brightnesses of the surface of the display. The term azimuth angle is to be understood here to mean the angle of the straight line formed by the intersection of the plane of incidence of the relevant beam of light with the reflected surface and the preferential direction of the structure of the surface. For some applications, for example in the case of clocks, it is desirable however that the surface of the display should retain its brightness even in the case of azimuth rotation, because in this way neither the aesthetic sense of the observer is upset nor is the readability adversely affected.
From DT-OS No. 2 531 372 is known a reflector for liquid crystal displays which employs a bubble-shaped structure for the reflector surface and which achieves a practically ideal brightness of the display surface practically independently of the azimuth angle. In the production of such a reflector, however, several process stages are necessary which bring about a considerable increase in the production costs of the reflector and make its use more difficult in the case of mass-produced products.